In the high speed production of steel bars or other elongated metal bars a heated billet is passed through a series of reducing rolls. In this process only a certain production can be achieved at any predetermined delivery speed. To increase production for a given speed of delivery a technique has been developed of rolling a billet to form two or more strands interconnected by a continuous node or nodes and then slitting the bar by passing the node or nodes longitudinally over the edge of fixed knives. Such knives are, however, subject to wear and must be replaced frequently, causing expense and loss in production time. This wear can be minimized by using rotating knives or knife-like rolls which do not substantially change the shape or cross-sectional area of the bars. However, such wear cannot be eliminated.
It has been known to separate interconnected strands by passing them between a pair of opposing rolls which cause adjacent strands to be offset vertically relative to one another, thereby shearing the node or web and separating the strands. This method may result in a product of inferior quality.
It has also been known to separate interconnected strands by passing them between a pair of rolls which reduce the cross-sectional area of adjacent strands by different amounts thus causing them to exit from the roll stand at different velocities, the speed differential in turn inducing a longitudinal force in the node which results in ruptures and strand separation. This method is not well suited to modern continuous rolling mills because the separated strands are not presented to subsequent stands in the desired form, namely simultaneously and at substantially identical velocities. Furthermore, this method can only be used in a mill which is equipped with twin looping tables.
It is an object of the present invention to provide an improved method of longitudinally slitting a double or triple stranded bar which does not require the continuous operation of slitting knives.
It is a further object of the present invention to provide an improved method of longitudinally slitting a double or triple stranded bar without vertical shearing.
It is a further object of the present invention to provide an improved method of longitudinally slitting a double or triple stranded bar which will produce a finished bar of high quality.
It is still another object of the invention to provide an improved method of longitudinally slitting a double or triple stranded bar, which method may be used in a modern high speed continuous rolling mill including such a mill which may be normally equipped for single strand operation having single looping tables in the finishing train.